There is a commercial requirement for packaging materials, especially films for packaging edible products, which exhibit barrier properties, particularly oxygen and water barrier. Existing commercially available packaging films consist of a multiplicity of layers, generally comprising a metallic or polyvinylidene chloride layer to provide the required barrier, particularly oxygen barrier, properties. However, there is presently a perceived requirement for more environmentally acceptable materials than polyvinylidene chloride resins. In addition, coating materials which are less energy intensive than metal, such as aluminium, are required.
Coated materials comprising layer minerals are known. The layer minerals have been used to impart a variety of properties to film substrate materials, such as flame retardancy, antistatic property and gas, particularly oxygen, barrier, as disclosed, for example in Japanese Unexamined Patent Application No 62-181144, EP-A-235926 and U.S. Pat. No. 3,499,820.
Japanese Unexamined Patent Application No 63-233836 discloses a polymeric film having steam and gas barrier properties comprising a coating layer of a laminar silicate and a vinylidene chloride resin.
One particular type of commercially available packaging material, is a film laminate or composite sheet comprising, in order, substrate layer (e.g. polyester film)/polyvinylidene chloride (or metal) coating layer/thermoset polyurethane adherent layer/heat-sealable (e.g. polyethylene) layer.
Unfortunately, when the polyvinylidene chloride (or metal) coating layer, in the aforementioned laminate structure is replaced by a layer mineral coating layer, poor adhesion is observed between the layer mineral layer and the heat-sealable layer, even when the intermediate thermoset polyurethane adherent layer is employed.